N

• Naturally occurring radioactive materials

  Collection of ionising radiation that exists in natural form in the environment, resulting from cosmic or terrestrial radioactive sources.

• Neutron

  Elementary particle with no electric charge that is part of the nucleus of atoms; its mass is 1.00136 times that of the proton.

• Nuclear chain reaction

  Series of similar nuclear reactions that take place because one of the agents causing the reaction (usually a neutron) is the product of another of these reactions.

• Nuclear fission

  Nuclear reaction where a heavy nucleus splits, usually into two fragments whose size has the same order of magnitude, and in which neutrons are emitted and a large amount of energy is released.

• Nuclear fuel cycle

  Series of industrial operations that fissionable materials are subjected to so that they can be used in a nuclear reactor. It includes from the mining stage to irradiated fuel management.

• Nuclear fusion

  Reaction between nuclei of light atoms that leads to the formation of a nucleus heavier than the initial ones, accompanied by the emission of elementary particles and energy.

• Nuclear medicine

  Use of radioisotopes, such as encapsulated and non-encapsulated sources, with medical diagnostic or therapy purposes. They are used "in vivo" (nuclear medicine services) or "in vitro" (radioimmune analysis laboratories).

• Nuclear power plant

  Electric power production plant that uses fissile material to obtain heat through nuclear reactions.

• Nuclear reaction

  Reaction between particles where the intervening forces are of nuclear origin.

• Nuclear reactor

  Facility where a nuclear chain reaction can be initiated, maintained and controlled. The pressurised water (nuclear) reactor is cooled with natural water at a pressure higher than saturation pressure in order to prevent it from boiling. The boiling water reactor is cooled with natural water, which is left to boil in the core in considerable quantities.

• Nuclear risk / undue risk

  Nuclear damage contingency. If this risk is higher than the admissible level it is called undue risk.

• Nuclear safety

  Collection of rules and practices used for the location, project, control and operation of nuclear or radioactive facilities with no undue risk.

• Nuclear substance

  In Spanish legislation, name applied to nuclear fuel, except for natural uranium and depleted uranium, and to radioactive products and waste.

• Nuclide

  Atomic species (collection of identical atoms) characterised by the number of protons and neutrons it has.